[ATM] Phase contrast and the 10 incher.

[Dale Eason <atmpob@yahoo.com>]

I have improved my phase contrast technique and now
present this closeup view of the 10F5 with the so
called worm tracks.

High resolution version: 800K
http://home.comcast.net/~doeason/Phase_contrast/Highres_interior_10F5.jpg

Original version:
http://home.comcast.net/~doeason/phase_and_foucault.jpg


I have also learned a little more about some of the
features seen in the images.  All of the finger prints
in the high res version are on the back.  The stair
step almost linear scratches right of center are on
the front.  The circular core can be seen close to the
center.  It was not cut all the way through and some
sort of material probably plaster was poured into the
saw kurf.  One of the worm tracks crosses over into
the core.  So the worm tracks are probably either on
or close to the surface.

Texereau has what may be similar worm track images in
his second edition page 62 photo C.  He says they are
veins in the glass.  Several of you said the same
thing.  So the worm track are probably inside the
glass.

Texereau also shows a rippled surface in picture D on
that page and later again on page 90.  These he
attributes to a honeycomb foundation lap.  The maker
of the 10 inch F5 mirror told me he used honeycomb and
barnsite on a Draper machine. 

Phase contrast Technique improvements:
I learned to measure my phase strip density.  It was
only 1.45.  Texereau says images on page 90 were taken
with strips of 1.6 and 2.81.   My high resolution
image above was taken with a 2.4 density phase strip
and a 200mm zoom F3.5 at 200mm and a 2X tele extender.
 Exposure time was 2 seconds at ISO 200.

Dale Eason




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